This invention relates to improved fire resistant hydraulic fluids and more particularly to silicone-base hydraulic fluids having improved antiwear properties.
The currently used petroleum-base, military aircraft, hydraulic fluid, which conforms to Military Specification MIL-H-5606C is an extremely flammable material. This material, which was developed in the early phases of World War II, possesses all of the desired properties of a good hydraulic fluid with the one exception of fire resistance. Hydraulic systems in military aircraft under combat or operational conditions are subject to projectile damage or component failures which could result in the release of this fluid under pressures as high as 3,000 psi in the form of a spray or a jet. In the presence of an ignition source, a hazardous condition or fire may result, causing aircraft damage or loss and a threat to crew safety. It is clear then that military aircraft survivability can be improved by reducing their vulnerability to hydraulic fluid induced fires resulting from enemy ground fire, accidents, and system malfunctions. To this end fire resistant silicone-base hydraulic fluids have been developed. Fire resistant silicone base hydraulic fluids must not only possess the desirable properties of high flash point and high fire points but must also possess other properties which ideally equal or surpass the requirements set forth in MIL-H-5606C. For obvious reasons, one of the chief characteristics such fluids must possess is superlative antiwear properties.